After the terrorist attacks in Paris on Friday night that left at least 129 people dead and hundreds more injured, the hacking collective Anonymous posted a video in which a person claiming to represent the group said, "Anonymous from all over the world will hunt you down."

"We will launch the biggest operation ever against you," the masked person said. "Expect massive cyberattacks. War is declared. Get prepared."

A Telegram channel that is believed to be affiliated with ISIS hackers then sent out a message to its followers instructing them how to keep from getting hacked by Anonymous.

"The #Anonymous hackers threatened in new video release that they will carry out a major hack operation on the Islamic state (idiots)," the statement read in part.

ISIS then asks "What they gonna hack?" noting that so far Anonymous had hacked only ISIS-affiliated Twitter accounts and emails.

The message went on to provide "instructions" on how to avoid potential hacks: Don't open any links unless sure of the source. Change IP addresses "constantly." And "do not talk to people [you] don't know on Telegram" or through Twitter direct messaging.

The message, which was posted in both Arabic and English, was then forwarded around to various other ISIS-affiliated Telegram channels.

Anonymous started targeting extremists in January after the terrorist attacks on the satirical French magazine Charlie Hebdo. The hackers worked to identify ISIS-linked social-media accounts and take down extremist websites.

ISIS supporters also used Telegram channels affiliated with the group to coordinate a social-media response to the Paris attacks on Friday: